Belt tensioners are used to impart a load on a belt. The belt load prevents the belt from slipping on one or more entrained pulleys during operation. Typically the belt is used in an engine application for driving various accessories associated with the engine. For example, an air conditioning compressor and alternator are two of the accessories that may be driven by a belt drive system.
A belt tensioner comprises a pulley journalled to an arm. A spring is connected between the arm and a base. The spring may also engage a damping mechanism. The damping mechanism comprises frictional surfaces in contact with each other. The damping mechanism damps an oscillatory movement of the arm caused by operation of the belt drive. This in turn enhances belt life expectancy.
In order to increase fuel economy and efficiency, many automotive manufacturers are beginning to incorporate alternators with the capability to drive the accessory belt drive system (ABDS). Such alternators are commonly referred to motor generator units (MGU's) or belt starter generators (BSG's). These can be used to start the engine, charge the battery, or boost the vehicle. During standard operation, the crankshaft pulley drives the ABDS. When this is the case, the tight side is the side of the belt that is entering the crank pulley, and the slack side is the side that is coming off of the crank pulley. However, when the MGU is used to drive the system (such as during starting), the tight side becomes the side of the belt entering the MGU, and the slack side is the side of the belt leaving the MGU and entering the crank pulley.
Representative of the art is U.S. Pat. No. 9,140,338 which discloses a tensioner comprising a base, a first pivot arm pivotally engaged to the base, a first pulley journalled to the first pivot arm, a second pivot arm pivotally engaged to the base, a second pulley journalled to the second pivot arm, a flexible tensile member having a toothed engagement with the first pivot arm and a toothed engagement with the second pivot arm whereby the first pivot arm and the second pivot arm move in a coordinated manner, and a tensioner assembly pivotally engaged to the base and engaged with the flexible tensile member.
What is needed is a tensioner having a first sub-assembly cooperatively engaged with a second sub-assembly through an elongate flexible member and a one-way clutch, a first torsion spring and a second torsion spring exert a tensile load on the elongate flexible member, and the one-way clutch frictionally engaged with a first pivot arm whereby a relative movement of the first pivot arm away from a second pivot arm is restricted. The present invention meets this need.